The ability to interconnect computers and other intelligent devices is a common requirement wherever people live and work today. The electrical connection required to form this local area network (LAN) has traditionally been accomplished by installing dedicated data wiring both inside buildings and between clusters of buildings. A number of wireless (i.e. radio) methods have also been developed and deployed to address this need.
Well-established power distribution systems exist throughout most of the United States, and other countries, which provide power to customers via power lines. With some modification, the infrastructure of the existing power distribution systems can be used to provide data communication in addition to power delivery, thereby forming a power line communication (PLC) system. This infrastructure can also be used to establish residential or office-based networks using the pre-existing wiring already present on the premises.
PLC, also known as Broadband Power Line (BPL), is a technology that encompasses transmission of data at high frequencies through existing electric power lines, i.e., conductors used for carrying a power current. Power current is typically transmitted through power lines at a frequency in the range of 50-60 hertz (Hz). In low voltage lines, power current is transmitted with a voltage between about 90 to 600 volts, and in medium voltage lines, power current is transmitted with a voltage between about 2,400 volts to 35,000 volts. Power Line Carrier (PLC) technology typically uses modulated radio frequency (RF) signals between about 1 MHz and 30 MHz, which are conducted on the power wiring to transport the data. The voltage of the data signal ranges from a fraction of a volt to a few tens of volts. Data communication can employ various modulation schemes such as amplitude modulation, frequency modulation, pulse modulation or spread spectrum modulation.
There are significant practical advantages offered by PLC technology—namely that electrical wiring, of necessity, must be installed and that data connectivity can therefore be immediately added at little (or no) additional cost, particularly in existing buildings. Similarly, electrical outlets are ubiquitous within modern buildings and significant operating convenience is realized when data is simultaneously available at every outlet. Another advantage of PLC technology is that the range that can be achieved is significantly greater than wireless methods, particularly in commercial buildings constructed of heavier materials that severely attenuate wireless signals.
Techniques for home networking over residential, low voltage, power lines have received considerable attention in recent years. The HomePlug Powerline Alliance, for example, has established a high-speed PLC networking standard that operates at RF frequencies between about 1 and 30 MHz. Currently, several manufacturers such as Intellon and Conexant are producing and marketing PLC devices for the consumer market that are interoperable under HomePlug standards. HomePlug is developing a new specification, HomePlug A/V, which will operate upward in frequency to somewhere near 30 MHz. The transmission technique employed by HomePlug 1.0 and HomePlug A/V (HPAV) is Orthogonal Frequency Division Multiplexing (OFDM).
A device that is to communicate over a PLC network such as a personal computer, media server, and the like, plugs into a conventional AC outlet to establish a communication path. While this can be a convenient arrangement for many such devices, it is inconvenient when the device to be networked does not use AC power as its primary energy source but rather is powered by a battery or other DC source. For instance, many portable MP3 players, digital cameras, and PDAs use a battery (rechargeable as well as non-rechargable) as their primary energy source and thus do not have an appropriate AC connector (except of course possibly an AC connector that is used to recharge the battery).
High voltage power lines are also used in PLC networks for communication purposes. While generally it is not practical to directly connect a communication device to high power conductors, in some cases it may be necessary. For instance, a technician servicing a problem with data transmission over a high power line may need to monitor the PLC network at various points along it without affecting the existing connections on the power lines. In this case, the technician will be observing activity on the network rather than establishing a two-way connection.
Accordingly, it would be desirable to provide for both residential, business and other purposes a method and apparatus for connecting a device, particularly a battery-powered device, to a PLC network without using an AC connection.